Items, such as projectiles, are made by either forging or by casting. These items contain not only an exterior surface, but also an internal cavity. At times, it is necessary to perform various operations on the exterior surface, such as chucking, grinding and machining or turning. When such operations are desired, the item to be worked on must be either secured in a stationary position so that the operations can be performed on the stationary item or the item must be secured to a moving apparatus so that a moving or stationary apparatus can perform the operations. In either of these cases, the item to be worked on must be secured and put in a desired position.
There are three possible avenues available to secure the item. One approach is to grip the exterior of the item. Unfortunately, when this is done, the apparatus for gripping the item can get in the way of and interfere with the performance of the desired operation. For example, if the item is clamped and is being finished with a fine grinder, the clamps will interfere with the grinding device. To complete the finishing operation, the clamps must be removed and relocated. This additional step, if not done exactly, can cause a lack of uniformity in the dimensional finish and can ruin the item. It is, nonetheless, a step preferably avoided.
Another approach is to add a piece of material, a component or a handle device to either or both the interior and the exterior of the item during casting or forging. In such cases, the apparatus gripping the item grabs the extra material, component or separate handle device while an operation, such as grinding, is being performed on the item. However, as with the previous examples, the introduction of this extra element may interfere with the operations. Moreover, in most circumstances the extra element will have to be removed prior to finalizing the item. Again, such an additional step may affect the quality or performance of the final product. There is the further aspect with this approach of waste in that the extra material or separate handle must be removed and disposed of. In some circumstances, this extra component can be recycled.
Finally, a third approach is to grip the interior chamber of the item to be worked on. This can be difficult in that oftentimes the throat of the internal cavity is smaller in cross sectional area than the cross sectional area of cavity's main section. In short, the throat typically has a smaller inside diameter than the chamber's main section. Other problems are also present because it is difficult to center the item during the gripping process.
There is therefore a significant need for efficiently gripping an item to be worked on that can also simultaneously center the object.